The present invention relates to a method of, and an apparatus for, manufacturing a cathode ray tube such as a color image receiving tube. More particularly, the invention relates to a method of, and an apparatus for, forming a high-resistance film on the neck section of a cathode ray tube, in which an electron gun is sealed.
Generally, a color image receiving tube has an envelope composed of a panel, a funnel and a neck, which are connected, forming an integral unit.
On the inner surface of the panel, a phosphor screen is provided. The phosphor screen has a number of segments, each consisting of three phosphor stripes or dots for emitting three different colors, respectively. A shadow mask is provided in the envelope, opposing the inner surface of the phosphor screen. The shadow mask has a number of apertures.
In the neck, an electron gun is provided. The electron gun is designed to emit three electron beams, which travel in the same horizontal plane. The electron gun has a main electron lens that has a low-voltage grid and a high-voltage grid. Each grid has a hole for guiding the center beam and two holes for guiding the two side beams. The holes for guiding the side beams, made in the low-voltage grid, are eccentric to the holes for guiding the side beams, made in the high-voltage grid, so that the three electron beams may be focused and converged at the center of the phosphor screen.
Outside the funnel, a deflection yoke is provided for deflecting the three electron beams the electron gun has emitted. The deflection yoke generates a horizontal deflection magnetic field and a vertical deflection magnetic field. These magnetic fields deflect the electron beams, so that the beams may scan the phosphor screen in horizontal and the vertical directions, after passing through the apertures of the shadow mask. Thus scanned with the electron beams, the phosphor screen displays a color image.
A high-resistance film is formed on the inner surface of the neck there is formed a high-resistance film, and an inner conductor film is formed on the inner surface of the funnel. The high-resistance film has a higher resistance than the inner conductor film and is connected thereto. The high-resistance film inhibits changes (known as xe2x80x9ccharge-upxe2x80x9d) in the potential of the inner surface of the neck, that may occur when the dispersed electrons leaking through the gap between the grids impinge upon the inner surface of the neck. Namely, the high-resistance film formed on the inner surface of the neck inhibits a charge-up, thereby to stabilize the neck potential. Since the high-resistance film thus provided suppresses the changes in the neck potential, the paths of the side beams are preventing from changing in the horizontal direction in the gaps between the grids. In other words, the high-resistance film can reduce so-called xe2x80x9cconvergence drift.xe2x80x9d
The high-resistance film formed on the inner surface of the neck must have an extremely high resistance. In addition, its resistance must remain stable. Otherwise, the high-resistance film can not stabilize the neck potential.
To this end, the high-resistance film may be made of material having high resistance (e.g., chromium oxide or the like). The resistance of such a substance, however, greatly depends on temperature. That is, the resistance changes very much as the operating temperature or ambient temperature of the color image receiving tube changes. This is a problem.
In order to solve the problem, the inventors hereof have proposed a method of forming a high-resistance film, in Jpn. Pat. Appln. KOKAI Publication No. 10-134739. This method consists in coating the inner surface of the neck with a liquid composed of a solvent such as alcohol and conductive particles of tin oxide or the like dispersed in the solvent, thereby forming a high-resistance film. To disperse the conductive particles uniformly in the solvent, however, the solvent must have a relatively low viscosity. To make matter worse, the particles dispersed in the solvent are far more electrically conductive than chromium oxide or the like. As a consequence, the resistance of the high-resistance film depends on the thickness of the film.
Dip method or spray method may be employed to form a high-resistance film having a desired thickness uniformity. In the dip method, the neck is immersed in the liquid and lifted therefrom, thereby forming a high-resistance film on the inner surface of the neck. In the spray method, the liquid is sprayed onto the inner surface of the neck, thereby forming a high-resistance film thereon.
The dip method is disadvantageous in three respects. First, a much complicated apparatus must be used to perform this method, increasing the manufacturing cost of the high-resistance film. Second, the efficiency of coating is low because the amount of the liquid actually applied to the inner surface of the neck is much smaller than the pool of the liquid in which the neck is dipped. Third, the pool of the liquid is liable to contamination, and the resultant film deteriorates in quality once the pool has been contaminated.
The spray method is disadvantageous, too. The liquid is sprayed onto the inner surface of the neck. Thus, it is applied in the form of mist. The mist of the liquid diffuse in the neck, and the liquid may be applied to those parts of the neck, which need not be covered with the high-resistance film.
At present, no method are available that can form a high-resistance film of a desired thickness uniformity on the inner surface of the neck. Any high-resistance film having no desired thickness uniformity has its resistance changed with temperature, failing to inhibit the charge-up of the neck potential. As a consequence, the high-resistance film can not reduce the convergence drift.
The present invention has been made in view of the foregoing. Its object is to provide a method of, and an apparatus for, manufacturing a cathode ray tube, in which a high-resistance film can be formed to a desired thickness on the inner surface of the neck of a tube and can therefore reduce the convergence drift caused by the charge-up of the neck potential.
To attain the object, the present invention provide a method of manufacturing a cathode ray tube comprising: an electron gun comprising an electron beam generating section for generating a plurality of electron beams which travel parallel in a horizontal plane and a plurality of electrodes spaced apart in a direction in which the electron beams travel, each electrode having a plurality of holes for guiding the electron beams; a deflection yoke for generating magnetic fields which deflect the electron beams emitted from the electron gun, in horizontal and vertical directions of a target; an envelope including a neck section which contains the electron gun, a panel section on which the target is provided, and a funnel section which connects the neck section and the panel section and which has an inner diameter flaring from the neck section to the panel section; an inner conductive film provided on an inner surface of a junction between the funnel section and the neck section; and a high-resistance film formed by coating on an inner surface of the neck section, contacting the inner conductive film, covering a part the electron gun and having a resistance higher than the inner conductive film, the method comprising the steps of: arranging the envelope, with the neck section extending in a substantially vertical direction; supplying a liquid material for forming the high-resistance film; and ejecting the liquid material toward the inner surface of the neck, such that the liquid is applied to the inner surface of the neck along a line inclined to a plane perpendicular to the inner surface of the neck, toward a direction of gravity, thereby to form the high-resistance film on the inner surface of the neck section.
To achieve the object described above, the invention provide an apparatus for manufacturing a cathode ray tube comprising: an electron gun comprising an electron beam generating section for generating a plurality of electron beams which travel parallel in a horizontal plane and a plurality of electrodes spaced apart in a direction in which the electron beams travel, each electrode having a plurality of holes for guiding the electron beams; a deflection yoke for generating magnetic fields which deflect the electron beams emitted from the electron gun, in horizontal and vertical directions of a target; an envelope including a neck section which contains the electron gun, a panel section on which the target is provided, and a funnel section which connects the neck section and the panel section and which has an inner diameter flaring from the neck section to the panel section; an inner conductive film provided on an inner surface of a junction between the funnel section and the neck section; and a high-resistance film formed by coating on an inner surface of the neck section, contacting the inner conductive film, covering a part of the electron gun and having a resistance higher than the inner conductive film, the apparatus comprising: envelope-arranging means for arranging the envelope, with the neck section extending in a substantially vertical direction; liquid-supplying means for supplying a liquid material for forming the high-resistance film; and liquid-applying means for ejecting the liquid material toward the inner surface of the neck, such that the liquid is applied to the inner surface of the neck along a line inclined to a plane perpendicular to the inner surface of the neck, toward a direction of gravity, thereby to form the high-resistance film on the inner surface of the neck section.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.